Removal of sulfur from carbonaceous fuels

ABSTRACT

The sulfur content of solid carbonaceous fuels, such as coal or lignite, is reduced by reacting a portion of the fuel with oxygen and steam without complete carbonization of the fuel, so as to generate nascent hydrogen at the surface and within the fuel particles for reaction with the sulfur in the fuel to form hydrogen sulfide. The resulting sulfur containing gases are removed and a low sulfur, solid fuel is recovered which can be burned, without further treatment or use of special devices, in furnaces or other combustion equipment with production of stack gases which meet pollution regulations regarding sulfur emissions. Alternatively, the low sulfur solid fuel may be gasified to produce low sulfur fuel gases or gases for the manufacture of industrial chemicals.

United States Patent Schroeder Sept. 30, 1975 i 1 REMOVAL OF SULFUR FROMPrimary ExaminerCarl F. Dees CARBONACEOUS FUELS Attorney, Agent, orFirm-Bacon & Thomas [76] Inventor: Wilburn C. Schroeder, 7316 RadcliffeDr., College Park, Md. [571 ABSTRACT 20740 The sulfur content of solidcarbonaceous fuels, such as Filed: June 1973 coal or ligmte, is reducedby reacting a portion of the [52] US. Cl 44/1 R; 201/17 [51] Int. Cl.C10L 9/02; ClOL 9/08; ClOB 57/00 [58] Field of Search 44/] R; 201/17;208/8 [56] References Cited UNITED STATES PATENTS 2,595,366 5/l952 Odellet al. 201/17 2,608,526 8/1952 Rex t 208/8 2,772,265 11/1956 Siddiqui20l/l7 3,824,084 7/l974 Dillon et a1. 44/1 R fuel with oxygen and steamwithout complete carbonization of the fuel, so as to generate nascenthydrogen at the surface and within the fuel particles for reaction withthe sulfur in the fuel to form hydrogen sulfide. The resulting sulfurcontaining gases are removed and a low sulfur, solid fuel is recoveredwhich can be burned, without further treatment or use of specialdevices, in furnaces or other combustion equipment with production ofstack gases which meet pollution regulations regarding sulfur emissions.Alternatively, the low sulfur solid fuel may be gasified to produce lowsulfur fuel gases or gases for the manufacture of industrial chemicals.

17 Claims, 3 Drawing Figures U.S. Patent PEFCE N T SULFUR IQEMOVEDPEACE/V T SUL FUR PE I0 VED Sept. 30,1975

Sheet 1 of 2 EFFECT OF PRESSURE IN REACT/ON Zfl/V' 0N SULFUR REMOVAL FPO7 CWHL PEQCENT (U/4L CU/VVEIQTED 70 GAS REMOVAL OF SULFUR FROMCARBONACEOUS FUELS This invention relates to a process for reducing thesulfur content of solid carbonaceous fuels, such as coal and lignite, toprovide a solid fuel product which can be burned, without furthertreatment or use of special devices, in furnances or other combustionequipment and which will produce stack gases which meet pollutionregulations regarding sulfur emissions. The solid sulfur-containing fuelis contacted with air or oxygen and with steam under conditionsresulting in generation of nascent hydrogen for reaction with the sulfurof the fuel without complete carbonization of the fuel. The sulfur isremoved as hydrogen sulfide. in this application of the invention toreduce the sulfur content of fuels the nitrogen content of the fuel isalso reduced to some extent, which assists in the control of nitrgoenoxide emissions whenthe fuel is burned.

The invention further provides a solid fuel which can be gasified withair to produce a gaseouos fuel under pressure, which gaseous fuel is lowin sulfur and in particulate matter, and suitable for use in a gasturbine or a combined cycle consisting of a gas turbine followed by asteam cycle.

It is a further purpose of the invention to provide a solid fuel whichcan be gasified with oxygen and steam under pressure to produce a gashigh in CO and H and which can be used to produce liquid fuels,alcohols, and other oxygenated hydrocarbons, ammonia. and pipeline gas.

The manner in which the fuel is used for these purposes will be madeevident in the following description of the invention.

A variety of methods have been suggested to reduce the discharge ofsulfur compounds into the atmosphere when sulfur containing fuels suchcoal are burned for heating purposes or to produce steam for thegeneration of electric power. Two general methods have been tried. Thefirst attempts to remove the sulfur from the stack gases after thesulfur containing fuel is burned, the second attempts to remove thesulfur from the fuel before it is burned.

One of the simplest methods proposed to remove sulfur from the stackgases is to add limestone to the furnace where it is calcined to CaO,which in turn reacts with the SO: in the stack gases to form solid CaSOwhich can be taken out in the precipitators. This was not found to bevery effective and under good conditions was unable to remove more thanabout 30 percent of the SO; in the stack gases. Also the precipitatorsbecame less effective when the S Concentration in the stack gases wasreduced. Some furnaces could not operate well with the additional amountof solid and the disposal of the solid was a further problem.

Another method tested was to pass the stack gas through wet scrubbersbefore it was discharged into the air. Various types of slurry orsolutions for scrubbing the gases were used such as those containinglimestone or lime. dolomite. magnesium oxide or other alkalinematerials. These were found to be 50-70 percent effective in removingthe sulfur compounds from the stack gases.

Many problems were encountered with the scrubbing methods. The scrubberswere unreliable and plugged up. so that either the combustion gas had tobe bypassed or the furnace shut down. Corrosion problems were severe andcontrol of conditions in the scrubber was difficult. The combustiongases were cooled by scrubbing and would not rise into the air afterleaving the exit stack and it was often necessary to reheat the stackgases. Disposal of solids from the scrubbing tower was a difficultproblem. One of the most serious problems was that a multiplicity ofscrubbers was needed and the gas cleaning installation required about asmuch space as the power plant. Installation costs and operating expenseswere high.

Numerous other methods have been and are being tried for stack gascleaning but none appears to be simple or low cost. The inherentdifficulties are the enormous volume of stack gas that must be processedand the very low concentration of $0 in these gases.

The problem with stack gas cleaning have resulted in attempts to removethe sulfur compounds from coal before it is burned. If this issuccessful, than fuel can be burned as it has been in the past, withoutmaterial change in the operation of furnaces, boilers and utilityplants.

About percent of the coal used in industrial furnaces is now cleaned invarious density separation or washing processes. This helps to reducethe iron sulfide content of some coals but does not eliminate theorganic sulfur. On many coals, especially those east of the MississippiRiver, the washing processes have not generally reduced the sulfursufficiently to meet pollution requirements.

Attempts have been made to dissolve or disperse the coal in solvents,such as aromatic compounds produced from the coal, and then filter offthe undissolved material which contains most of the sulfur compounds.The solution process is often carried out under hydrogen pressure whichprobably aids in dissolving the coal. After filtration the solution isrecovered for reuse by distillation from the solid fuel. The plant andequipment for carrying out this process are complex and costly, and thefiltration step and the recovery of the solvent are especially difficultproblems. Also a substantial residue of combustible material is leftwhich is both high in ash and sulfur. This material must either bediscarded and waster or burned and then the sulfur removed from thecombustion gases.

Complete hydrogenation of the coal to liquid products can be carried outand this will produce an oil very low in sulfur. The process is highlycomplex and the capital cost of the equipment is high, which leads to ahigh cost product.

The gasification of coal or coke with steam and air or oxygen to producecombustible gases has been practiced for over 50 years. When steam andair are used a low Btu gas is produced having a heating value of lSO toBtu per cubic foot. With steam and oxygen the heating value is from 300to 350 Btu per cubic foot. Either of these gases can be purified toremove sulfur. and then burned in a furnace.

The present invention differes from gasifieation as practiced heretoforeby reacting only the minimum amount of coal with steam and air (oroxygen) which is necessary to reduce the sulfur in the coal to thedesired level, and all the remaining coal is removed from the reactionzone. The desulfurized coal still contains sufficient volatile matter sothat it is a satisfactory fuel for combustion purposes. The product isnot a coke or char. [t has been carbonized only to the extend necessaryto remove a substantial amount of the sulfur.

Complete gasification as practiced heretofore requires the necessaryequipment and facilities for converting all the coal (or coke) to gasand the capital cost is high. The purification process to remove H 8 isalso large and costly because of the large volume of gas passing throughthe equipment. The operation of this equipment to produce gas from coalincreases fuel costs from 2.5 to 3 times the cost of the coal itself. In

'oth'erwords, with coal costing $0.30 per million Btu,

. one-tenth of the cost for gasification. The purification step isalsoreduced accordingly. Operating costs are greatly reduced and it isestimated that they will increase fuel costs only by l5 to percent overthe cost of the coal. With coal at $0.30 per million Btu the cost of thefuel (desulfurized coal and gas) would be from $0.34 to $0.36 permillion Btu. The heat loss in the process is to 8 percent.

The desulfurized coal from the process, containing volatile matter asheretofore noted, is a fuel commonly used in utility boilers. On theother hand, the gas from a gasification process is of much lower Btucontent per 7 cubic foot than natural gas and has not been used inutility boilers. This is especially true for gas made with steam andair. Such gas cannot be used in existing boilers without considerablyloss in capacity.

In addition to the gasification of coal, processes to treat coal withsteam and air or oxygen to substantially completely Carbonize the coalto produce a coke or char are well known and are described in manypatents. Methods for treatment of the coke or char with hydrogen orother reducing gas to lower the sulfur content of the char have alsobeen practiced. Hydrogen or other reducing gas for treatment of the charhas been generated externally or internally. Internal generation ofhydrogen or reducing gas has been done with air or oxygen and steam.

None of these processes, however, has been performed in one single stepwhich heats the coal, desulfurizes the coal under optimum conditions,provides a maximum amount of coal for subsequent combustion steps,provides coal which is not carbonized but which instead contains a largeamount of volatile matter, making it most suitable for subsequentcombustion processes, carries out the desulfurization process withminirnum use of air or oxygen at the lowest reaction temperatures, anduses a minimum amount of coal in the desulfurization step. Because ofthe small amount of coal consumed in the process the H 8 is contained ina relatively small amount of gas from which it is easily removed. Theproduct gases are combustible gases which are valuable for subsequentcombustion processes.

Furthermore, the invention can be used on strongly caking bituminouscoals, non-caking subbituminous coals, or lignite. The coal particle,without previous thermal treatment of any kind, is introduced into a bedof particles at operating temperature, which heats the coal particlerapidly. Combustion with oxygen at the particle surface provides furtherheat for rapid expansion of the particle and creation of large surfaceareas.

The increased porosity of the particle as well as its large surface areamake the hydrogen more effective in sulfur removal.

The coal particle heats and expands in the presence of steam whichreacts with the hot carbon to produce nascent hydrogen which is highlyeffective in reacting with sulfur or sulfur compounds to produce H 5.The H S is carried out with the other gaseous'constituents and removedfrom the gas by well known purification methods.

Temperatures, nascent hydrogen production, and coal-throughput are allcontrollable, and are so controlled that they provide maximum sulfurremoval,

minimum change in the coal itself, and minimum heat loss. The result isa process which is low in captial investment and operating cost andgives minimum increase in fuel cost over the cost of the coal itself.The coal product can be used in existing boilers or in new boilerswithout the addition of spacial facilities to the boiler itself andwithout loss of steam output and without change in the method ofoperating the boiler.

None of the prior known processes operates in such a manner as toproduce a high yield of low sulfur coal containing substantial volatilematter.

This invention achieves these results by converting the sulfur or sulfurcompounds in the coal to H 8. This is done by generating hydrogenthrough reaction of a small amount of the coal with steam (either addedor generated from the moisture in the coal) at elevated temperature, asfollows:

Part of the coal is burned with air (or oxygen) to create favored bypreheating both the air (or oxygen) and steam used in thedesulfurization process.

The invention as further illustrated in the accompanying drawings,wherein:

FIG. 1 is a graft showing the effect of pressure in the reaction zone onsulfur removal from coal.

FIG. 2 is a graft showing the percent of coal converted to gas vs.sulfur removal.

FIG. 3 is a flow diagram showing representative steps in processesutilizing the invention.

The temperature required depends on the types of coal and the amount ofsulfur to be removed. The bituminous coals prevalent in the eastern andmidwestern parts of the United States often contains from 2.5 to

' over 4 percent sulfur. To meet pollution requirements it is generallynecessary to reduce the sulfur to below one percent. The temperaturerequired is in the range from ll00 to l300F,although it may go as highas 1500F for the low volatile butuminous coals.

The western coals are lower in sulfur, often close to one percent, andare subbituminous coals with most of the sulfur present or organicsulfur. Temperatures in the range from 900 to 1400F will usually reducethe sulfur in these coals to the required levels.

In the process all the coal particles pass through the heated zone andare subjected to the action of the hot hydrogen and CO produced at thecoal surface, thereby reducing the sulfur in the particle to H5. Thecoal parti'cle then passes out of the reactor as a low sulfur fuel whichcan subsequently be burned in a furnace and the resulting combustiongases will be low enough to sulfur to meet pollution controlregulations.

The temperature is controlled by the amount of air (or oxygen) and steamadmitted for a given coal flow through the reactor. More air increasesthe temperature. More stem decreases the temperature but generates morehydrogen. The amount of hydrogen produced is very important. At a givenoperating temperature, sulfur removal can be increases by increasing thehydrogen concentration considerably beyond the stoichiometric hydrogenrequired.

In addition to this hydrogen formed by the reaction of hot carbon andsteam some hydrogen is also released from the coal particle as it isbrought to high temperature. In general coals contain 4 to 5 percent byweight of hydrogen and some of this forms hydrogen gas. It is believedthat this hydrogen also helps in removal of the sulfur from the coal.

It has been found that the generation of hydrogen (and CO) at thesurface of and within the coal particle is much more effective thanpassage of hydrogen (and CO) from an external source through the hotcoal particles. Under atmospheric pressure in the reaction zone,hydrogen or hydrogen and CO from external sources has little effect inremoving sulfur from the coal. At increased pressure some sulfur wasremoved but the amount was very small compared to the amount removedwhen the CO and hydrogen were generated at the surface of the coalparticle. It is believed that the favorable conditions for sulfurremoval result from the action of the nascent hydrogen which is producedand exists momentarily at the reacting gas-coal interface.

It is important to keep the temperature as low as possible and stillsecure satisfactory sulfur removal from the coal, especially if thedesulfurized coal is to be used in an industrial or utility furnace forsteam raising. Coal containing ten or more percent volatile matter burnsmuch more rapidly than coal which has been almost completelydevolatilized or coal which has been almost completely devolatilized orcoal which has been converted to coke or char, and most boilers aredesigned for a coal containing volatile matter. By using sufficientsteam to generate hydrogen in excess of that required to convert the Sto H 8 the volatile matter in coal can be kept well over 10 to 12percent.

Pressure has been found to be an important variable in the removal ofsulfur from coal and the process is sensitive to the total pressure atwhich the reactions are carried out, as shown in FIG. 1. A low volatilebituminous coal desulfurized at 1500F shows less than 40 percent sulfurremoval at atmospheric pressure but this increases to over 80 percentwhen the reactions are carried out under the same conditions at a totalpressure of 3 atmospheres.

Purification of the gas stream from the reaction zone removesparticulate matter, oils and tars, ammonia, and H 8. The gas is passedthrough a cyclone separator to remove as much particulate matter aspossible and this is recycled to the reactor. The gasis then cooled bothby heat exchange with incoming gas streams and a waste heat boiler toprovide steam for the process. This condenses the oils and tars whichalso carry with them most of the remaining particulate matter. Thisliquid and solid material contains sulfur and is recycled back to thereaction zone. The gas is then washed by direct contact with water whichremoves the ammonia and any remaining liquids or solids. Sulfur can beremoved from the cooled gas stream by several wellknown processes, suchas the hot potassium carbonate, or monoethanol amine.

Sulfur may be produced from the H 8 removed in the purification processby a Claus process plant which converts the H 5 to liquid or solidsulfur. The final purified gas is a combustible gas which can be burnedalong with the desulfurized coal, or which can be utilized for otherpurposes which will be described later.

The desulfurized coal recovered from the process will be the amount fedless the coal converted to gas. FIG. 2 shows the relationship betweenthe amount of coal converted to gas and sulfur removal for a bituminouscoal desulfurized at 1500F under 3 atmospheres pressure. About 8 percentof the coal is required to maintain bed temperatures. Reaction ofadditional coal then provides the hydrogen necessary fordesulfurization. The gasification of 12 percent of the coal removespercent of sulfur from the coal particles.

Desulfurized coal leaving the reaction zone is at high temperature. Inorder to avoid loss of the sensible heat the coal particles will betransformed hot to any subsequent combustion process.

I-Ieat losses in the process arise from the production of a small amountof CO and the cooling of the gas stream during purification. Both aresmall and it is estimated that the total heat loss (including the heatlost from not burning the sulfur) is approximately 8 percent.

In the desulfurization process described herein the use of catalysts onthe coal is unnecessary. It is wellknown however, that hydrogenationreactions can be favorably influenced by a large number of catalysts,which are usually metals or metal compounds. Some of the best catalystsare compounds of molybdenum and cobalt or mixtures of the two. These areeffective in very low concentrations but they are also expensive. Iron,tin, aluminum, and zinc are useful in somewhat higher concentrations andare less expensive. The catalysts may be applied by converting them towater soluble salts which can be sprayed onto the coal or the finelyground metallic compounds may be mixed with coal as solid materialsduring the pulyerization of the coal.

For coals which are found difficult to desilfurize the addition of acatalyst may increase the effectiveness of the process.

The gas stream leaving the reactor contains CO, H H 8, ammonia, volatilematter, some CO and oils and tars. If air was used in thedesulfurization process it also contains N It is important that theconcentration of H S in the gas be kept below one volume percent or thereactions to remove sulfur from the coal may be suppressed. Preferable,the concentration of H 8 is kept between about 0.1 and 0.5 percent. Thevolume of gases produced during gasification is usually too small tomaintain this low concentration of hydrogen sulfide. Additional gas maybe provided as necessary by recycling purified tail gas (after removalof hydrogen sulfide and ammonia) back to the reactor.

The major constituents in this recycle gas are H CO, and methane. Themethane is produced during the partial devolitization of the coal andfrom the reaction of the coal and hydrogen. The presence of the methanein the recycle gas is beneficial since it helps to suppress furthermethane formation from the coal.

The amount of steam fed to the reaction vessel should be sufficient toprovide hydrogen in excess of stoichiometric requirement for removal ofthe sulfur in the form of H 5. To reduce the sulfur in most coal toabout 0.5 weight percent in a short time, such as approximately 10minutes, has been found to require hydrogen concentrations at least 4 totimes stoichiometric. The use of superheated steam helps to reduce theheat requirements in the reactor, but this is not a major factor.

It should also be noted that some moisutre is present in the coal whichmust be taken into account in determining steam requirements. Thepresence of this moisture is desirable since it is distributedthroughout the coal particle and will release hydrogen by reaction withthe carbon as soon as the particle reaches a sufficiently hightemperature.

Drying of the coal is not desirable unless the moisture content exceedsthe amount required for the production of hydrogen. It is recognizedthat the moisture present in the coal requires combustion of some of thecoal to vaporize the water and to bring it to high temperature, but thisis not a heavy burden on the process.

In case the moisture in the coal is much in excess of that required tofurnish hydrogen the coal should be dried to the desired level before itis fed to the process.

The specific advantages of the coal desulfurization process which hasbeen described are as follows:

1. Sulfur is reduced or removed from crushed or pulverized coal, eithercaking or non-caking, without the addition of materials other than steamand air (or oxygen).

2. Operating pressures for sulfur removal are low and generally between1 and atmospheres.

3. The sulfur as H 5, (and some nitrogen as NH is evolved in arelatively small volume of gas from which it can readily be removed. Theconcentration of CO in the gas stream is low which simplifies theremoval of H S and final conversion of the sulfur compounds to sulfur.

4. The solid fuel produced in the process is low in sulfur and may betransferred hot to utility or industrial furnaces and burned in the samemanner coal is burned.

-5. Both the solid and gaseous fuel from the process can can be producedunder pressure and would therefore be useful for complete conversion togaseous fuel under pressure for use in a gas turbine. The resultinggaseous fuel would be low in sulfur compounds.

6. The reduction of the sulfur content in the coal necessary for a 1000MW utility plant may be accomplished by passing the coal through 2 to 4vessels.

The invention will be further understood from the following exampleshaving reference to FIG. 3 of the drawings.

EXAMPLE 1 Crushed or pulverized coal is fed continuously through line 10at a controlled rate to vessel 1 by gravity, screw conveyor, or othersuitable means, and partly devolatized coal is withdrawn from the bottomthrough line 2. Vessel l is steel, refractory lined to withstandinternal temperatures up to about 1700F. It is also well insulated onthe inside to reduce heat loss. A portion of the coal in vessel 1 isburned continuously by passage of steam and air (or oxygen), admittedthrough line 3, through coal bed 4. Recycle gas is also fed to coal bed4 through line 3 as needed.

Air, steam and recycle gas fed to vessel 1 may be blown upwardly througha pulverized coal bed. For a bed of crushed coal the air, steam andrecycle gas may be blown upward or downward, since crushed coal may beheld on a grate near the bottom of vessel 1. Steam is fed as necessaryto produce hydrogen.

For strongly caking bituminous coals it is necessary to recycle coalfrom near the bottom of bed 4 to the top, to prevent agglomeration ofthe bed by the introduction of the fresh coal. For this purpose, thecoal is withdrawn through line 5 and is lifted to the top of the bed bya small amount of steam and air entering through line 9.

The gas generated leaves the reactor through line 6 and passes throughcyclone spearator 7. Solid material from the bottom of the separator 7is returned to coal bed 4.

The most suitable temperature to be maintained in vessel 1 depends onthe coal, rate of throughput, and degree of desulfurization desired.Bituminous coal requires higher temperatures and longer retention timesthan subbituminous coals or lignite. In most cases bituminous coals willrequire retention times from 8 to 10 minutes and temperatures in therange from 1 l00-l 500F. Retention times for subbituminous coal andlignite are from about 4 to 8 minutes at temperatures of 900l 400F. Thepressure in the reaction vessel is in the range of from atmospheric upto about 10 atmospheres. Optimum pressures for desulfurization are inthe range of 2 to 6 atmospheres.

To heat one ton of coal to 1200l 500F, decompose steam, and react thesulfur and some of the nitrogen compounds with hydrogen requires thecombustion of approximately 180 to 250 lbs. of coal. The resultingvolume of combustion gas is generally between 20,000 and 40,000 standardcubic feet when air and steam are used desulfurization. Methods forpurification of the gas stream remove better than 99.5 percent of H 3present in the gas.

Taking as an example a coal with a proximate analysis as follows:

Weight Percent The amount of air required to desulfurize this coal toabout 0.5% sulfur is about 20,000 standard cubic feet and the amount ofsteam is from about to 140 lbs. per tonof dry coal. The amount of pureoxygen required to desulfurize this same coal to 0.5% sulfur is about4,000' standard cubic feet per ton of coal.

The percent of sulfur eliminated from the coal will depend on the coal,sulfur in the coal, temperature. pressure and time the coal is attemperature. Rate of coal feed, time, temperature, pressure, and amountof hydrogen released care controlled in accordance with this invention.If the resulting fuel is to be used for combustion purposes theelimination of 80 to percent of sulfur in coals containing not more than3 or 3.5 to begin with is satisfactory. It has been found that retentiontimes of less than ten minutes in the temperature zone are satisfactory.

During the desulfurization n of the coal -40 percent of the nitrogenwill be converted to NH and carried out with the gas steam. This isadvantageous from the standpoint of helping to eliminate nitrogen oxideformation when the coal is burned. Nitrogen in the fuel contributessubstantially to nitrogen oxide formation in the stack gases, and it isbelieved to be an important contributor even in comparison with thenitrogen in the air used for combustion.

The gas from cyclone separator 7 passes through line 11 to cooler 12where the temperature is reduced to about 400F. Cooler 12 may be a heatexchanger, a waste heat boiler or a combination of both. Oils, tars, andsome solids will be removed from the gas stream by cooling. The gas thenpasses through line 13 to a water wash in vessel 14. This cools the gasto below 200F and also removes any NFL, in the gas. Any remainingparticulate matter is also removed. The gas then passes through line 15to an H 5 removal process which takes place as illustrated at 16.

Any one of several H 8 removal processes may be used, such as scrubbingwith hot potassium carbonate or monoethanol amine. The H 8 released fromsuch a process should not be vented to the air since thiswould causepollution. The H S may be treated in a Claus plant to produce liquid orsolid sulfur. Purification processes also may be used which will removethe H 5 and produce solid sulfur directly, such as the Giammarco-Vetrocoke or Stretford processes. After the gas is free of H 5 it isready for subsequent use in combustion or gasification equipment.

As shown in the drawing,the desulfurized coal from vessel 1 may be feddirectly to furnace 17 or to other types of solid fuel combustionequipment. For furnace equipment that burns coal in the pulverized form,the coal fed to vessel 1 should be pulverized and the desulfurizationzone in this vessel is operated as a fluidized solids zone. Theresulting product may then be used directly for combustion. A portion ofthe sulfur-free gases from 16 may be added to the pulverized coalthrough line 17(a) if desired. The remainder is recycled to the vessel1, as shown.

If the fuel is fed directly from vessel 1 to the combustion equipment itwill be approximately at the temperature of the desulfurization zone. Inthis case most of the heat used in bringing the coal to thedesulfurization temperature will be recovered, and the net heat loss inthe desulfurization process will be very small.

The solid fuel from vessel 1 which is used in this manner is low insulfur and nitrogen compounds but still contains the major portion ofthe ash which was in the coal. The combustion equipment in which thisfuel is used must therefore be equipped with electrostitic precipitatorsor cyclone separators to prevent the discharge of particulate matterwith the combustion gases.

EXAMPLE 2 A gaseous fuel under pressure and free from particulate matteras well as low in ash. and sulfur. is prepared as follows:

Referring again to FIG. 3 of the drawings, vessel 1 is operated under apressure of 10 to atmospheres. Coal or solid fuel is fed into vessel 1by a suitable system (not shown), preferably as disclosed in my pendingapplication Serial No. 268,202,f1led June 30, I972 entitled Methods andApparatus for Feeding Finely Divided Solids to a Pressurized Gas orGas-Liquid-Solids System." In addition, the gas purification cyclerepresented by vessels 7, 12, 14 and 16 is also operated under pressureand the sulfur free gas product is under pressure.

The solid fuel from vessel 1 flows into vessel 18 without loss ofpressure'or temperature. In vessel 18 the solid fuel is gasified underpressure with air and steam to produce a gas which is largely CO and Hcontaining some volatile matter as well as the nitrogen from the air.The hot, pressurized gas from vessel 18 is freed of particulate matterin cyclone separators l9 and 20. The ash and unburned coal from thecyclone separators. may be recycled to vessel 18 through line 21 ifdesired. This will reduce unburned carbon in the ash.

The 'gas recovered in the sulfur removal step and released from vessel16 under pressure can not be joined with the gases from cycloneseparators 19 and 20. The combined gases under pressure are excellentfuel for a gas turbine or a combined cycle, such as a gas turbinefollowed by a steam cycle.

Alternatively, hydrogen and carbon monoxide gases low in sulfurcompounds and nitrogen can be prepared by gasifying the desulfurizedcoal in vessel 18 with steam and oxygen instead of steam and air; Inthis case the tail gas from vessel l6should not be added to this gasstream since it contains nitrogen.

Hydrogen and carbon monoxide gas are used in the production ofindustrial materials such as ammonia, urea, alcohols, and pipeline gas.In addition, these products may be used to make liquid products such asgasoline, diesel oil and jet fuels. I

During the past 30 years most of the H and CO necessary for theseindustrial chemicals has been made from natural gas and oil. Shortagesof these fuels makes it highly desirable to substitute coal for oil andgas and the present invention makes this possible in a relatively simpleand thermally efficient process.

Processes using H and CO operate under pressures ranging from 10 to 15atmospheres up to about 200 atmospheres. In general it is most efficientto generate the gases at the operating pressure of the processes.

EXAMPLE 3 If it is desired to produce a tail gas which is nitrogen freethe process is operated as follows: referring again to FIG. 3, vessel 1is operated at the desired pressure with coal fed to the system aspreviously described. Stea and oxygen are used instead of steam and airto desulfurize the coal. The hot solid product from vessel 1 is passedto gasification vessel 22 without cooling.

Gasification of the desulfurized coal is carried out in vessel 22 underpressure with oxygen and steam. High temperature steam may be used toincrease the H content of the gas. Depending upon the final products tobe made, the tail gas from vessel 16 may be combined with the productgas from gasifier 22 (e.g. if pipeline gas is to be made) or may be fedto gasifier 22 so that the gas will be converted entirely to CO and HGases from vessel 22 are freed of particulate matter in cycloneseparators 23 and 24 and are ready for use. At this point they are hotand still under pressure. If it is necessary to cool the gases to somelow temperature for processing, this should be done in a waste heatboiler or other system that will recover as much useful energy aspossible.

I claim:

1. A process for reducing the sulfur content of naturally-occurring,sulfurcontaining, solid carbonaceous fuel to less than 1.0 percent,comprising reacting said fuel in particulate form under a pressure of atleast 2 atmospheres with an oxygen-containing gas and with steam in areaction zone, the amount of oxygencontaining gas beingjust sufficientto burn a portion of said fuel to raise the temperature of the fuel insaid zone to about llOO to 1500F. and the steam being present in anamount sufficient to react with the fuel particles to generate nascenthydrogen at the surface and within said particles and form hydrogensulfide with the sulfur therein, removing the sulfur containing gasesfrom said zone and recovering the fuel of reduced sulfur content.

2. The process of claim 1 wherein the pressure in the reaction zone isbetween 2 and 6 atmospheres.

3. The process of claim 1 wherein no more than about 14% of the fuel isconsumed by the reaction with oxygen and steam.

4. The process of claim 1 wherein the fuel is a bituminous coal andwherein the recovered desulfurized coal retains at least 10 percentvolatile matter.

5. The process of claim 1 wherein the residence time of the fuel in thereactor is less than about 12 minutes.

6. The process of claim 1 wherein the amount of hydrogen in contact withthe fuel is about 4 to 5 times the amount theoretically required toreact with all of the sulfur in the fuel to form H 8.

7. The process of claim 1 wherein the fuel is bituminous coal, thetemperature in the reaction zone is from about 1 100 to 1500F and theresidence time of the coal particles in the reaction zone is from about8 to 10 minutes.

8. The process of claim 1 wherein the fuel is subbituminous coal, thetemperature in the reaction zone is about 900 to 1400F and the residencetime of the coal particles in the reaction zone is from about 4 to 8minutes.

9. The process of claim 1 wherein the sulfur containing gases arepurified to remove sulfur and the purified tail gas which issubstantially free of sulfur is recycled to the reaction zone tomaintain the sulfur content of the gases in this zone between about 0.1to 0.5 volume percent.

10. The process of claim 1 wherein the recovered fuel withoutsubstantial reduction in temperature is reacted in a separate reactionzone to generate heat or produce fuel gases.

11. The process of claim 1 wherein the recovered fuel is gasified in aseparate reaction zone to produce low sulfur fuel gases.

12. The process of claim 11 wherein the sulfur containing gases producedin the initial reaction zone are purified to remove sulfur and areintroduced into said separate reaction zone with the recovered sulfurfree fuel. I

13. The process of claim 11 wherein the sulfur containing gases producedin the initial reaction zone are purified to remove sulfur and arecombined with the gases from said separate reaction zone.

14. The process of claim 11 wherein the separate reaction zone is'undera pressure of 2 to 300 atmospheres, the pressure in the initial reactionzone is at least as high as that of said separate reaction zone, and thehot desulfurized fuel is transferred from said first reaction zone tothe separate reaction zone without substantial loss of temperature orpressure.

15. The process of claim 1 wherein the oxygen containing gas is air.

16. The process'of claim 1 wherein the oxygen containing gas is oxygenor oxygen enriched air.

17. A process for desulfurizing sulfur-containing coal comprisingreacting said coal in particulate form with oxygen and steam in areaction zone'under a pressure of at least 2 atmospheres, the amount ofoxygen being just sufficient to burn a portion of the coal to raise thetemperature in said zone to about 900* to 1500F and the amount of steambeing sufficie'nt to react with the coal to generate nascent hydrogen incontact with the coal, the amount of hydrogenincluding that generated bythe steam reaction and that present in the coal being about 4 to 5 timesthat theoretically required for reaction with all of the sulfur in thecoal to produce H S, removing the sulfur-containing gases from saidzone, purifying said sulfur-containing gases to provide a substantiallysulfur-free tail gas, recycling the sulfur free tail gas to saidreaction zone to maintain the sulfur content of the gases in contactwith the coal below about 0.5 volume percent, and removing thedesulfurized coal from said zone after a residence time of less thanabout 12 minutes.

1. A PROCESS FOR REDUCING THE SULFUR CONTENT OF NATURALLYOCCURING,SULFUR-CONTAINING, SOLID CARBONACEOUS FUEL TO LESS THAN 1.0 PERCENT,COMPRISING REACTING SAID FUEL IN PARTICULATE FORM UNDER A PRESSURE OF ATLEAST 2 ATMOSPHERES WITH AN OXYGEN-CONTAINING GAS AND WITH STEAM IN AREACTION ZONE, THE AMOUNT OF OXYGEN-CONTAINING GAS BEING JUST SUFFICIENTTO BURN A PORTION OF SAID FUEL TO RAISE THE TEMPERATURE OF THE FUEL INSAID ZONE TO ABOUT 1100* TO 1500*F. AND THE STEAM BEING PRESENT IN ANAMOUNT SUFFICIENT TO REACT WITH THE FUEL PARTICLES TO GENERATE NASCENTHYDROGEN AT THE SURFACE AND WITHIN SAID PARTICLES AND FORM HYDROGENSULFIDE WITH THE SULFUR THEREIN, REMOVING THE SULFUR CONTAINING GASESFROM SAID ZONE AND RECOVERING THE FUEL OF REDUCED SULFUR CONTENT.
 2. Theprocess of claim 1 wherein the pressure in the reaction zone is between2 and 6 atmospheres.
 3. The process of claim 1 wherein no more thanabout 14% of the fuel is consumed by the reaction with oxygen and steam.4. The process of claim 1 wherein the fuel is a bituminous coal andwherein the recovered desulfurized coal retains at least 10 percentvolatile matter.
 5. The process of claim 1 wherein the residence time ofthe fuel in the reactor is less than about 12 minutes.
 6. The process ofclaim 1 wherein the amount of hydrogen in contact with the fuel is about4 to 5 times the amount theoretically required to react with all of thesulfur in the fuel to form H2S.
 7. The process of claim 1 wherein thefuel is bituminous coal, the temperature in the reaction zone is fromabout 1100* to 1500*F and the residence time of the coal particles inthe reaction zone is from about 8 to 10 minutes.
 8. The process of claim1 wherein the fuel is subbituminous coal, the temperature in thereaction zone is about 900* to 1400*F and the residence time of the coalparticles in the reaction zone is from about 4 to 8 minutes.
 9. Theprocess of claim 1 wherein the sulfur containing gases are purified toremove sulfur and the purified tail gas which is substantially free ofsulfur is recycled to the reaction zone to maintain the sulfur contentof the gases in this zone between about 0.1 to 0.5 volume percent. 10.The process of claim 1 wherein the recovered fuel without substantialreduction in temperature is reacted in a separate reaction zone togenerate heat or produce fuel gases.
 11. The process of claim 1 whereinthe recovered fuel is gasified in a separate reaction zone to producelow sulfur fuel gases.
 12. The process of claim 11 wherein the sulfurcontaining gases produced in the initial reaction zone are purified toremove sulfur and are introduced into said separate reaction zone withthe recovered sulfur free fuel.
 13. The process of claim 11 wherein thesulfur containing gases produced in the initial reaction zone arepurified to remove sulfur and are combined with the gases from saidseparate reaction zone.
 14. The process of claim 11 wherein the separatereaction zone is under a pressure of 2 to 300 atmospheres, the pressurein the initial reaction zone is at least as high as that of saidseparate reaction zone, and the hot desulfurized fuel is transferredfrom said first reaction zone to the separate reaction zone withoutsubstantial loss of temperature or pressure.
 15. The process of claim 1wherein the oxygen containing gas is air.
 16. The process of claim 1wherein the oxygen containing gas is oxygen or oxygen enriched air. 17.A process for desulfurizing sulfur-containing coal comprising reactingsaid coal in particulate form with oxygen and steam in a reaction zoneunder a pressure of at least 2 atmospheres, the amount of oxygen beingjust sufficient to burn a portion of the coal to raise the temperaturein said zone to about 900* to 1500*F and the amount of steam beingsufficient to react with the coal to generate nascent hydrogen incontact with the coal, the amOunt of hydrogen including that generatedby the steam reaction and that present in the coal being about 4 to 5times that theoretically required for reaction with all of the sulfur inthe coal to produce H2S, removing the sulfur-containing gases from saidzone, purifying said sulfur-containing gases to provide a substantiallysulfur-free tail gas, recycling the sulfur free tail gas to saidreaction zone to maintain the sulfur content of the gases in contactwith the coal below about 0.5 volume percent, and removing thedesulfurized coal from said zone after a residence time of less thanabout 12 minutes.